From wood pellets to wood chips, risks of degradation and emissions from the storage of woody biomass – A short review

Abstract

The compounds in stored woody biomass degrade as a result of chemical and/or biological processes during storage. These processes produce gaseous emissions. Recent studies concerning gaseous emissions from wood pellet storages are reviewed herein. The applicability of the results from pellet research to wood chips is discussed. Thorough scientific understanding on the storage phenomena of wood chips is extremely important as the threat of climate change and the need to reduce greenhouse gas emissions have led to an increased need to large scale wood chip storage to ensure supply. Typically the gases produced from stored woody biomasses are carbon monoxide (CO), carbon dioxide (CO 2), methane (CH 4), and other volatile hydrocarbons e.g. aldehydes and terpenes. CO 2 and CH 4 are greenhouse gases with high global warming potential. Chemical degradation via auto-oxidation of fats and fatty-acids seems to be the dominant mechanism for off-gassing from stored wood pellets, whereas biological processes are mainly responsible for the gaseous emission from wood chips. In confined storage spaces gaseous emissions may lead to oxygen depletion. Oxygen depletion together with a high CO concentration poses a serious health risk for those working in such conditions. The degradation processes also result in dry matter losses and in spontaneous heating and in the worst case, especially in large piles, spontaneous ignition of the stored material. Thorough and systematic scientific studies on degradation processes and their effects are needed in order to understand and minimise risks from large scale wood chips storage to human health, environment and property.

Effect of particle granularity on smoldering fire in wood chips made from wood waste: An experimental study

“…Biomass is increasingly acknowledged as an important renewable energy source, and wood chips is an example of a bio‐based feed material for waste‐to‐energy plants. However, self‐heating (without ignition), auto‐ignition, dust explosions, long‐lasting smoldering fires, and toxic gas formation are the key fire hazards related to the storage of wood chips . The thermal energy in self‐heating of piles of biomass waste is produced by biological and biochemical degradation, and may be catalyzed by the presence of impurities (eg, metal pieces) .…”

Evaluation, ranking and positioning of measurement methods for pellet production

“…Studies confirm that the storage time of raw materials has effects to the finished product quality parameters [12]. Microbiological and chemical processes are the root causes of this effect -which are dependent of the raw material molecular structure, elemental composition and moisture content, as well as of the storage mode and conditions [13] [14].…”

Factors affecting the utilization of lignocellulosic biomass; compaction, handling and storage, and monetary value – a review.

“…The danger of gaseous emissions has only been recently addressed after several fatalities involving CO poisoning (Alakoski et al 2016). The revelation of this risk has resulted in the need to retrofit many non-ventilated residential pellet store rooms in Europe, where toxic or fatal CO levels often accumulate (Emhofer et al 2014).…”

“…The revelation of this risk has resulted in the need to retrofit many non-ventilated residential pellet store rooms in Europe, where toxic or fatal CO levels often accumulate (Emhofer et al 2014). Alakoski et al (2016) conducted a short review on the gaseous emissions of pellets, with the following findings. The gaseous emissions of compacted biomass results in the reduction of quality through dry matter losses.…”